Add ft-gazed, the gaze service, and ft-gazectl

ft-gazed runs ft-gaze, drops blinks and dropouts, smooths with a fixation
lock, applies the probe's calibration plus what the pointer has taught
since, and sends the corrected gaze to the pointer helper at 90 Hz. The
helper sends lessons back (a nudge before a click), which are learned and
saved. It only reads the eye tracker; nothing of SteamVR's is written.
gaze/run.sh installs it as a user service that starts with SteamVR;
ft-gazectl turns gaze mode on and off and shows the service's status.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

gaze/ft-gazectl

@@ -0,0 +1,54 @@
+#!/usr/bin/python3
+"""ft-gazectl: turn the gaze pointer on or off, and ask the gaze service how it's doing.
+
+  ft-gazectl on|off|toggle   gaze mode in the pointer helper (until it restarts; the
+                             setting is POINTER_GAZE in ~/.config/frametop.conf)
+  ft-gazectl status          the gaze service (ft-gazed): samples, lessons, the correction
+  ft-gazectl forget          drop what the pointer's lessons taught (the calibration stays)
+  ft-gazectl reload          the service reads calibration.json again
+"""
+
+import json
+import os
+import socket
+import sys
+
+
+def ask(name, msg, timeout=1.0):
+    s = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM | socket.SOCK_CLOEXEC)
+    s.bind(f"\0ft_gazectl.{os.getpid()}")
+    s.settimeout(timeout)
+    try:
+        s.sendto(msg.encode(), "\0" + name)
+        return s.recv(4096).decode()
+    except ConnectionRefusedError:
+        return None
+    except socket.timeout:
+        return ""
+    finally:
+        s.close()
+
+
+def main():
+    cmd = sys.argv[1] if len(sys.argv) > 1 else "status"
+    if cmd in ("on", "off", "toggle"):
+        r = ask("ft_pointer_helper", f"gaze {cmd}")
+        if r is None:
+            sys.exit("the pointer helper isn't running")
+        print(f"gaze mode {r.removeprefix('ok ')}" if r else "no answer (an older pointer helper without gaze mode?)")
+        if ask("ft_gazed", "status", 0.3) is None:
+            print("note: the gaze service (ft-gazed) isn't running, so the pointer has no gaze to follow")
+    elif cmd in ("status", "forget", "reload"):
+        r = ask("ft_gazed", cmd)
+        if r is None:
+            sys.exit("the gaze service (ft-gazed) isn't running")
+        try:
+            print(json.dumps(json.loads(r), indent=1))
+        except ValueError:
+            print(r)
+    else:
+        sys.exit(__doc__)
+
+
+if __name__ == "__main__":
+    main()